Memory device comprising conductive pillars and method of forming the same

ABSTRACT

A memory device includes a multi-layer stack, a channel layer, a memory material layer and at least three conductive pillars. The multi-layer stack is disposed on a substrate and includes a plurality of conductive layers and a plurality of dielectric layers stacked alternately. The channel layer penetrates through the plurality of conductive layers and the plurality of dielectric layers. The memory material layer is disposed between the channel layer and each of the plurality of conductive layers and the plurality of dielectric layers. The conductive pillars are surrounded by the channel layer and the memory material layer, wherein the at least three conductive pillars are electrically connected to conductive lines respectively.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of U.S. provisionalapplication Ser. No. 63/040,538, filed on Jun. 18, 2020. The entirety ofthe above-mentioned patent application is hereby incorporated byreference herein and made a part of this specification.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment. Semiconductor devices are typically fabricated bysequentially depositing insulating or dielectric layers, conductivelayers, and semiconductor layers over a semiconductor substrate, andpatterning the various material layers using lithography and etchingtechniques to form circuit components and elements thereon.

The semiconductor industry continues to improve the integration densityof various electronic components (e.g., transistors, diodes, resistors,capacitors, etc.) by continual reductions in minimum feature size, whichallow more components to be integrated into a given area. However, asthe minimum features sizes are reduced, additional problems arise thatshould be addressed.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A, 1B, and 1C illustrate a simplified perspective view, a circuitdiagram, and a top down view of a memory device in accordance with someembodiments.

FIGS. 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13A, 13B, 14A, 14B, 15A, 15B,16A, 16B, 17A, 17B, 18A, 18B, 19A, 19B, 20A, 20B, 21A, 21B, 22A, 22B,23A, 23B, 24A, 24B, 25, 26A, 26B, 27A, 27B, 27C and 27D illustratevarying views of manufacturing a memory device in accordance with someembodiments.

FIG. 28 illustrates a simplified perspective view of a memory device inaccordance with alternative embodiments.

FIGS. 29A and 29B illustrates simplified perspective views of a memorydevice in accordance with alternative embodiments.

FIGS. 30A to 30C illustrate varying top down views of manufacturing amemory device in accordance with some embodiments.

FIG. 31 illustrates a top down view of a memory cell of a memory devicein accordance with alternative embodiments.

FIG. 32 illustrates a top down view of a memory cell of a memory devicein accordance with alternative embodiments.

FIG. 33 illustrates a top down view of a memory cell of a memory devicein accordance with alternative embodiments.

FIG. 34 illustrates a top down view of a memory cell of a memory devicein accordance with alternative embodiments.

FIG. 35 illustrates a method of forming a memory device in accordancewith some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Various embodiments provide a memory device such as a 3D memory array.In some embodiments, the 3D memory array is a ferroelectric field effecttransistor (FeFET) memory circuit including a plurality of verticallystacked memory cells. In some embodiments, each memory cell is regardedas a FeFET that includes a word line region acting as a gate electrode,a bit line region acting as a first source/drain electrode, a sourceline region acting as a second source/drain electrode, a ferroelectricmaterial acting as a gate dielectric, and an oxide semiconductor (OS)acting as a channel region. In some embodiments, each memory cell isregarded as a thin film transistor (TFT).

FIGS. 1A, 1B, and 1C illustrate examples of a memory array according tosome embodiments. FIG. 1A illustrates an example of a portion of asimplified memory device 200 in a partial three-dimensional view; FIG.1B illustrates a circuit diagram of the memory device 200; and FIG. 1Cillustrates a top down view of the memory device 200 in accordance withsome embodiments. The memory device 200 includes a plurality of memorycells 202, which may be arranged in a grid of rows and columns. Thememory cells 202 may be further stacked vertically to provide a threedimensional memory array, thereby increasing device density. The memorydevice 200 may be disposed in the back end of line (BEOL) of asemiconductor die. For example, the memory array may be disposed in theinterconnect layers of the semiconductor die, such as, above one or moreactive devices (e.g., transistors) formed on a semiconductor substrate.

In some embodiments, the memory device 200 is a flash memory array, suchas a NOR flash memory array, or the like. In some embodiments, a gate ofeach memory cell 202 is electrically coupled to a respective word line(e.g., conductive line 112), a first source/drain region of each memorycell 202 is electrically coupled to a respective bit line (e.g.,conductive line 128A1), a second source/drain region of each memory cell202 is electrically coupled to a respective source line (e.g.,conductive line 128B), and a third source/drain region of each memorycell 202 is electrically coupled to a respective bit line (e.g.,conductive line 128A2). The memory cells 202 in a same horizontal row ofthe memory device 200 may share a common word line while the memorycells 202 in a same vertical column of the memory device 200 may share acommon source line and common bit lines.

The memory device 200 includes a plurality of vertically stackedconductive lines 112 (e.g., word lines) with dielectric layers 52disposed between adjacent ones of the conductive lines 112. Theconductive lines 112 extend in a direction parallel to a major surfaceof an underlying substrate (not explicitly illustrated in FIGS. 1A and1C). The conductive lines 112 may have a staircase configuration suchthat lower conductive lines 112 are longer than and extend laterallypast endpoints of upper conductive lines 112. For example, in FIG. 1A,multiple, stacked layers of conductive lines 112 are illustrated withtopmost conductive lines 112 being the shortest and bottommostconductive lines 112 being the longest. Respective lengths of theconductive lines 112 may increase in a direction towards the underlyingsubstrate. In this manner, a portion of each of the conductive lines 112may be accessible from above the memory device 200, and conductivecontacts may be made to exposed portions of the conductive lines 112,respectively.

The memory device 200 further includes conductive pillars 106A (e.g.,electrically connected to first conductive lines), conductive pillars108 (e.g., electrically connected to second conductive lines) andconductive pillars 106B (e.g., electrically connected to firstconductive lines) arranged alternately. The conductive pillars 106B aredisposed between the conductive pillars 106A and the conductive pillars106B. The conductive pillars 106A, 106B and 108 may each extend in adirection perpendicular to the conductive lines 112. A dielectric pillar102 is disposed between and isolates adjacent ones of the conductivepillars 106A, 106B and the conductive pillars 108. The first conductiveline is one of a source line and a bit line, and the second conductiveline is the other of a source line and a bit line. In some embodiments,the conductive pillars 106A and the conductive pillars 106B areelectrically connected to bit lines, and the conductive pillars 108 areelectrically connected to source lines. In alternative embodiments, theconductive pillars 106A and the conductive pillars 106B are electricallyconnected to source lines, and the conductive pillars 108 areelectrically connected to bit lines.

Sets of the conductive pillars 106A, 106B and 108 along with anintersecting conductive line 112 define boundaries of each memory cell202, and the dielectric layer 120 is disposed between the adjacentconductive lines 112 (also referred to as common conductive lines 112).In some embodiments, the conductive pillars 108 are electrically coupledto ground. Although FIG. 1A illustrates a particular placement of theconductive pillars 106A, 106B relative the conductive pillars 108, itshould be appreciated that the placement of the conductive pillars 106A,106B and 108 may be exchanged in other embodiments.

In some embodiments, the memory device 200 include an oxidesemiconductor (OS) material as a channel layer 92. The channel layer 92may provide channel regions for the memory cells 202. For example, whenan appropriate voltage (e.g., higher than a respective threshold voltage(V_(th)) of a corresponding memory cell 202) is applied through acorresponding conductive line 112, a region of the channel layer 92 thatintersects the conductive line 112 allows current to flow from theconductive pillars 106A, 106B to the conductive pillars 108 (e.g., inthe direction indicated by arrow 206).

In some embodiments, a memory material layer 90 is disposed between thechannel layer 92 and each of the conductive lines 112 and the dielectriclayers 52, and the memory material layer 90 serves as a gate dielectricfor each memory cell 202. In some embodiments, the memory material layer90 includes a ferroelectric material, such as a hafnium oxide, hafniumzirconium oxide, silicon-doped hafnium oxide, or the like. In suchembodiments, the memory device 200 is also referred to as aferroelectric memory device. In alternative embodiments, the memorymaterial layer 90 include different types of memory materials. Forexample, the memory material layer 90 includes a non-ferroelectricmaterial, such as a multilayer memory structure including a layer ofSiNx between two SiOx layers (e.g., an ONO structure).

The memory material layer 90 may be polarized in one of two differentdirections, and the polarization direction may be changed by applying anappropriate differential voltage across the memory material layer 90 andgenerating an appropriate electric field. The polarization may berelatively localized (e.g., generally contained within each boundariesof the memory cells 202), and a continuous region of the memory materiallayer 90 may extend across a plurality of memory cells 202. Depending ona polarization direction of a particular region of the memory materiallayer 90, a threshold voltage of a corresponding memory cell 202 varies,and a digital value (e.g., 0 or 1) can be stored. For example, when aregion of the memory material layer 90 has a first electricalpolarization direction, the corresponding memory cell 202 may have arelatively low threshold voltage, and when the region of the memorymaterial layer 90 has a second electrical polarization direction, thecorresponding memory cell 202 may have a relatively high thresholdvoltage. The difference between the two threshold voltages may bereferred to as the threshold voltage shift. A larger threshold voltageshift makes it easier (e.g., less error prone) to read the digital valuestored in the corresponding memory cell 202.

To perform a write operation on a memory cell 202 in such embodiments, awrite voltage is applied across a portion of the memory material layer90 corresponding to the memory cell 202. In some embodiments, the writevoltage is applied, for example, by applying appropriate voltages to acorresponding conductive line 112 (e.g., the word line) and thecorresponding conductive pillars 106A, 106B/108 (e.g., the bitline/source line). By applying the write voltage across the portion ofthe memory material layer 90, a polarization direction of the region ofthe memory material layer 90 may be changed. As a result, thecorresponding threshold voltage of the corresponding memory cell 202 mayalso be switched from a low threshold voltage to a high thresholdvoltage or vice versa, and a digital value may be stored in the memorycell 202. Because the conductive lines 112 intersect the conductivepillars 106A, 106B and 108, individual memory cells 202 may be selectedfor the write operation.

To perform a read operation on the memory cell 202 in such embodiments,a read voltage (a voltage between the low and high threshold voltages)is applied to the corresponding conductive line 112 (e.g., the wordline). Depending on the polarization direction of the correspondingregion of the memory material layer 90, the memory cell 202 may or maynot be turned on. As a result, the conductive pillars 106A, 106B may ormay not be discharged through the conductive pillar 108 (e.g., a sourceline that is coupled to ground), and the digital value stored in thememory cell 202 can be determined. Because the conductive lines 112intersect the conductive pillars 106A, 106B and 108, individual memorycells 202 may be selected for the read operation.

FIG. 1A further illustrates reference cross-sections of the memorydevice 200 that are used in later figures. Cross-section B-B′ is along alongitudinal axis of conductive lines 112 and in a direction, forexample, parallel to the direction of current flow of the memory cells202. Cross-section C-C′ is parallel to cross-section B-B′ and extendsthrough the conductive pillars 106A, the conductive pillars 108 and theconductive pillars 106B. Cross-section D-D′ is perpendicular tocross-section B-B′ and extends through the conductive pillars 106A andthe conductive pillars 106B. Subsequent figures refer to these referencecross-sections for clarity.

In FIG. 2 , a substrate 50 is provided. The substrate 50 may be asemiconductor substrate, such as a bulk semiconductor, asemiconductor-on-insulator (SOI) substrate, or the like, which may bedoped (e.g., with a p-type or an n-type dopant) or undoped. Thesubstrate 50 may be an integrated circuit die, such as a logic die, amemory die, an ASIC die, or the like. The substrate 50 may be acomplementary metal oxide semiconductor (CMOS) die and may be referredto as a CMOS under array (CUA). The substrate 50 may be a wafer, such asa silicon wafer. Generally, an SOI substrate is a layer of asemiconductor material formed on an insulator layer. The insulator layermay be, for example, a buried oxide (BOX) layer, a silicon oxide layer,or the like. The insulator layer is provided on a substrate, typically asilicon or glass substrate. Other substrates, such as a multi-layered orgradient substrate may also be used. In some embodiments, thesemiconductor material of the substrate 50 may include silicon;germanium; a compound semiconductor including silicon carbide, galliumarsenide, gallium phosphide, indium phosphide, indium arsenide, and/orindium antimonide; an alloy semiconductor including silicon-germanium,gallium arsenide phosphide, aluminum indium arsenide, aluminum galliumarsenide, gallium indium arsenide, gallium indium phosphide, and/orgallium indium arsenide phosphide; or combinations thereof.

FIG. 2 further illustrates circuits that may be formed over thesubstrate 50. The circuits include transistors at a top surface of thesubstrate 50. The transistors may include gate dielectric layers 302over top surfaces of the substrate 50 and gate electrodes 304 over thegate dielectric layers 302. Source/drain regions 306 are disposed in thesubstrate 50 on opposite sides of the gate dielectric layers 302 and thegate electrodes 304. Gate spacers 308 are formed along sidewalls of thegate dielectric layers 302 and separate the source/drain regions 306from the gate electrodes 304 by appropriate lateral distances. Thetransistors may include fin field effect transistors (FinFETs),nanostructure (e.g., nanosheet, nanowire, gate-all-around, or the like)FETS (nano-FETs), planar FETs, the like, or combinations thereof, andmay be formed by gate-first processes or gate-last processes.

A first inter-layer dielectric (ILD) 310 surrounds and isolates thesource/drain regions 306, the gate dielectric layers 302, and the gateelectrodes 304 and a second ILD 312 is over the first ILD 310.Source/drain contacts 314 extend through the second ILD 312 and thefirst ILD 310 and are electrically coupled to the source/drain regions306 and gate contacts 316 extend through the second ILD 312 and areelectrically coupled to the gate electrodes 304. An interconnectstructure 320 is over the second ILD 312, the source/drain contacts 314,and the gate contacts 316. The interconnect structure 320 includes oneor more stacked dielectric layers 324 and conductive features 322 formedin the one or more dielectric layers 324, for example. The interconnectstructure 320 may be electrically connected to the gate contacts 316 andthe source/drain contacts 314 to form functional circuits. In someembodiments, the functional circuits formed by the interconnectstructure 320 may include logic circuits, memory circuits, senseamplifiers, controllers, input/output circuits, image sensor circuits,the like, or combinations thereof. Although FIG. 2 discusses transistorsformed over the substrate 50, other active devices (e.g., diodes or thelike) and/or passive devices (e.g., capacitors, resistors, or the like)may also be formed as part of the functional circuits.

In FIG. 3 , a multi-layer stack 58 is formed over the structure of FIG.2 . The substrate 50, the transistors, the ILDs 310 and 312, and theinterconnect structure 320 may be omitted from subsequent drawings forthe purposes of simplicity and clarity. Although the multi-layer stack58 is illustrated as contacting the dielectric layers 324 of theinterconnect structure 320, any number of intermediate layers may bedisposed between the substrate 50 and the multi-layer stack 58. Forexample, one or more interconnect layers including conductive featuresin insulating layers (e.g., low-k dielectric layers) may be disposedbetween the substrate 50 and the multi-layer stack 58. In someembodiments, the conductive features may be patterned to provide power,ground, and/or signal lines for the active devices on the substrate 50and/or the memory device 200 (see FIGS. 1A and 1B). In some embodiments,one or more interconnect layers including conductive features ininsulating layers (e.g., low-k dielectric layers) are disposed over themulti-layer stack 58.

In FIG. 3 , the multi-layer stack 58 includes alternating layers ofsacrificial layers 53A-53D (collectively referred to as sacrificiallayers 53) and dielectric layers 52A-52E (collectively referred to asdielectric layers 52). The sacrificial layers 53 may be patterned andreplaced in subsequent steps to define conductive lines 112 (e.g., theword lines). The sacrificial layers 53 may include dielectric materials,such as silicon oxide, silicon nitride, silicon oxynitride, combinationsthereof, or the like. The dielectric layers 52 may include insulatingmaterials, such as silicon oxide, silicon nitride, silicon oxynitride,combinations thereof, or the like. The sacrificial layers 53 and thedielectric layers 52 include different materials with different etchingselectivities. In some embodiments, the sacrificial layers 53 includesilicon nitride, and the dielectric layers 52 include silicon oxide.Each of the sacrificial layers 53 and the dielectric layers 52 may beformed using, for example, chemical vapor deposition (CVD), atomic layerdeposition (ALD), physical vapor deposition (PVD), plasma enhanced CVD(PECVD), or the like.

Although FIG. 3 illustrates a particular number of the sacrificiallayers 53 and the dielectric layers 52, other embodiments may includedifferent numbers of the sacrificial layers 53 and the dielectric layers52. Besides, although the multi-layer stack 58 is illustrated as havingdielectric layers as topmost and bottommost layers, the disclosure isnot limited thereto. In some embodiments, at least one of the topmostand bottommost layers of the multi-layer stack 58 is a sacrificiallayer.

FIGS. 4 through 12 are views of intermediate stages in the manufacturinga staircase structure of the memory device 200, in accordance with someembodiments. FIGS. 4 through 12 are illustrated along referencecross-section B-B′ illustrated in FIG. 1A.

In FIG. 4 , a photoresist 56 is formed over the multi-layer stack 58. Insome embodiments, the photoresist 56 is formed by a spin-on techniqueand patterned by an acceptable photolithography technique. Patterningthe photoresist 56 may expose the multi-layer stack 58 in regions 60,while masking remaining portions of the multi-layer stack 58. Forexample, a topmost layer of the multi-layer stack 58 (e.g., thedielectric layer 52E) is exposed in the regions 60.

In FIG. 5 , the exposed portions of the multi-layer stack 58 in theregions 60 are etched using the photoresist 56 as a mask. The etchingmay be any acceptable etching process, such as a dry etch (e.g., areactive ion etch (RIE), a neutral beam etch (NBE), the like), a wetetch, the like, or a combination thereof. The etching may beanisotropic. The etching may remove portions of the dielectric layer 52Eand the sacrificial layer 53D in the regions 60 and define openings 61.Because the dielectric layer 52E and the sacrificial layer 53D havedifferent material compositions, etchants used to remove exposedportions of these layers may be different. In some embodiments, thesacrificial layer 53D acts as an etch stop layer while etching thedielectric layer 52E, and the dielectric layer 52D acts as an etch stoplayer while etching sacrificial layer 53D. As a result, the portions ofthe dielectric layer 52E and the sacrificial layer 53D may beselectively removed without removing remaining layers of the multi-layerstack 58, and the openings 61 may be extended to a desired depth.Alternatively, a time-mode etching process may be used to stop theetching of the openings 61 after the openings 61 reach a desired depth.In the resulting structure, the dielectric layer 52D is exposed in theregions 60.

In FIG. 6 , the photoresist 56 is trimmed to expose additional portionsof the multi-layer stack 58. In some embodiments, the photoresist 56 istrimmed by using an acceptable removing technique such as a lateraletching. As a result of the trimming, a width of the photoresist 56 isreduced and portions the multi-layer stack 58 in the regions 60 andregions 62 may be exposed. For example, top surfaces of the dielectriclayer 52D may be exposed in the regions 60, and top surfaces of thedielectric layer 52E may be exposed in the regions 62.

In FIG. 7 , portions of the dielectric layer 52E, the sacrificial layer53D, the dielectric layer 52D, and the sacrificial layer 53C in theregions 60 and the regions 62 are removed by acceptable etchingprocesses using the photoresist 56 as a mask. The etching may be anyacceptable etching process, such as a dry etch (e.g., RIE, NBE, thelike), a wet etch, the like, or a combination thereof. The etching maybe anisotropic. The etching may extend the openings 61 further into themulti-layer stack 58. Because the sacrificial layers 53D and 53C and thedielectric layers 52E and 52D have different material compositions,etchants used to remove exposed portions of these layers may bedifferent. In some embodiments, portions of the dielectric layers 52Eand 52D in the regions 62 and 60 are removed by using the photoresist 56as a mask and using the underlying sacrificial layers 53D and 53C asetch stop layers. Thereafter, the exposed portions of the sacrificiallayers 53D and 53C in the regions 62 and 60 are removed by using thephotoresist 56 as a mask and using the underlying dielectric layers 52Dand 52C as etching stop layers. In the resulting structure, thedielectric layer 52C is exposed in the regions 60, and the dielectriclayer 52D is exposed in the regions 62.

In FIG. 8 , the photoresist 56 is trimmed to expose additional portionsof the multi-layer stack 58. In some embodiments, the photoresist 56 istrimmed by using an acceptable removing technique such as a lateraletching. As a result of the trimming, a width of the photoresist 56 isreduced, and portions the multi-layer stack 58 in the regions 60, theregions 62, and regions 64 may be exposed. For example, top surfaces ofthe dielectric layer 52C are exposed in the regions 60; top surfaces ofthe dielectric layer 52D are exposed in the regions 62; and top surfacesof the dielectric layer 52E are exposed in the regions 64.

In FIG. 9 , portions of the dielectric layers 52E, 52D, and 52C and thesacrificial layers 53D, 53C, and 53B in the regions 60, the regions 62,and the regions 64 are removed by acceptable etching processes using thephotoresist 56 as a mask. The etching may be any acceptable etchingprocess, such as a dry etch (e.g., RIE, NBE, the like), a wet etch, thelike, or a combination thereof. The etching may be anisotropic. Theetching may extend the openings 61 further into the multi-layer stack58. Because the dielectric layers 52C-52E and the sacrificial layers53B-53D have different material compositions, etchants used to removeexposed portions of these layers may be different. In some embodiments,portions of the dielectric layers 52E, 52D and 52C in the regions 64, 62and 60 are removed by using the photoresist 56 as a mask and using theunderlying sacrificial layers 53D, 53C and 53B as etch stop layers.Thereafter, the exposed portions of the sacrificial layers 53D, 53C and53B in the regions 64, 62 and 60 are removed by using the photoresist 56as a mask and using the underlying dielectric layers 52D, 52C and 52B asetching stop layers. In the resulting structure, the dielectric layer52B is exposed in the regions 60; the dielectric layer 52C is exposed inthe regions 62; and the dielectric layer 52D is exposed in the regions64.

In FIG. 10 , the photoresist 56 is trimmed to expose additional portionsof the multi-layer stack 58. In some embodiments, the photoresist 56 istrimmed by using an acceptable removing technique such as a lateraletching. As a result of the trimming, a width of the photoresist 56 isreduced, and portions the multi-layer stack 58 in the regions 60, theregions 62, the regions 64, and regions 66 may be exposed. For example,top surfaces of the dielectric layer 52B are exposed in the regions 60;top surfaces of the dielectric layer 52C are exposed in the regions 62;and top surfaces of the dielectric layer 52D are exposed in the regions64; and top surfaces of the dielectric layer 52E are exposed in theregions 66.

In FIG. 11 , portions of the dielectric layers 52E, 52D, 52C, and 52B inthe regions 60, the regions 62, the regions 64, and the regions 66 areremoved by acceptable etching processes using the photoresist 56 as amask. The etching may be any acceptable etching process, such as a dryetch (e.g., RIE, NBE, the like), a wet etch, the like, or a combinationthereof. The etching may be anisotropic. The etching may extend theopenings 61 further into the multi-layer stack 58. In some embodiments,portions of the dielectric layers 52E, 52D, 52C and 52B in the regions66, 64, 62 and 60 are removed by using the photoresist 56 as a mask andusing the underlying sacrificial layers 53D, 53C, 53B and 53A as etchstop layers. In the resulting structure, the sacrificial layer 53A isexposed in the regions 60; the sacrificial layer 53B is exposed in theregions 62; the sacrificial layer 53C is exposed in the regions 64; andthe sacrificial layer 53D is exposed in the regions 66. Thereafter, thephotoresist 56 may be removed by an acceptable ashing or wet stripprocess.

In FIG. 12 , an inter-metal dielectric (IMD) 70 is formed over themulti-layer stack 58. The IMD 70 may be formed of a dielectric material,and may be deposited by any suitable method, such as CVD, PECVD,flowable CVD (FCVD), or the like. The dielectric materials may includephospho-silicate glass (PSG), boro-silicate glass (BSG), boron-dopedphospho-silicate glass (BPSG), undoped silicate glass (USG), or thelike. In some embodiments, the IMD 70 includes an oxide (e.g., siliconoxide or the like), a nitride (e.g., silicon nitride or the like), acombination thereof or the like. Other dielectric materials formed byany acceptable process may be used. Thereafter, a removal process isperformed to remove excess dielectric material over the multi-layerstack 58. In some embodiments, the removal process is a planarizationprocess, such as a chemical mechanical polish (CMP), an etch-backprocess, combinations thereof, or the like. The planarization processexposes the multi-layer stack 58 such that top surfaces of themulti-layer stack 58 and IMD 70 are level after the planarizationprocess is completed. The IMD 70 extends along sidewalls of thesacrificial layers 53B-53D and sidewalls of the dielectric layers52B-52E. Further, the IMD 70 may contact top surfaces of the sacrificiallayers 53A-53D and the dielectric layer 52E.

As shown in FIG. 12 , an intermediate and bulk staircase structure isthus formed. The intermediate staircase structure includes alternatinglayers of sacrificial layers 53 and dielectric layers 52. Thesacrificial layers 53 are subsequently replaced with conductive lines112, which will be described in details in FIGS. 24A through 26B. Lowerconductive lines 112 are longer and extend laterally past upperconductive lines 112, and a width of each of the conductive lines 112increases in a direction towards the substrate 50 (see FIGS. 1A and27D).

FIGS. 13A through 16B are views of intermediate stages in themanufacturing of a memory region and a channel region of the memorydevice 200, in accordance with some embodiments. In FIGS. 13A through14B, the bulk multi-layer stack 58 is patterned to form trenches 100therethrough. FIGS. 13A, 14A, 15A and 16A illustrate top-down views.FIGS. 13B, 14B, 15B and 16B are illustrated along referencecross-section C-C′ illustrated in FIGS. 13A, 14A, 15A and 16A (alsoalong reference cross-section C-C′ illustrated in FIG. 1A).

In FIGS. 13A and 13B, photoresist patterns 74 and underlying hard maskpatterns 72 are formed over the multi-layer stack 58. In someembodiments, a hard mask layer and a photoresist layer are sequentiallyformed over the multi-layer stack 58. The hard mask layer may include,for example, silicon nitride, silicon oxynitride, or the like, which maybe deposited by CVD, PVD, ALD, PECVD, or the like. The photoresist layeris formed by a spin-on technique, for example.

Thereafter, the photoresist layer is patterned to form photoresistpatterns 74 and trenches 76 between the photoresist patterns 74. Thephotoresist is patterned by an acceptable photolithography technique,for example. The trenches 76 may be any shape such as an oval-likeshape, a triangle-like shape, a rectangle-like shape and a polygon-likeshape. The patterns of the photoresist patterns 74 are then transferredto the hard mask layer to form hard mask patterns 72 by using anacceptable etching process, such as by a dry etch (e.g., RIE, NBE, thelike), a wet etch, the like, or a combination thereof. The etching maybe anisotropic. Thus, trenches 76 are formed extending through the hardmask layer. Thereafter, the photoresist patterns 74 may be optionallyremoved by an ashing process.

In FIGS. 14A and 14B, the patterns of the hard mask patterns 72 aretransferred to the multi-layer stack 58 using one or more acceptableetching processes, such as by a dry etch (e.g., RIE, NBE, the like), awet etch, the like, or a combination thereof. The etching processes maybe anisotropic. Thus, the trenches 76 extend through the bulkmulti-layer stack 58. The hard mask patterns 72 may be then removed byan acceptable process, such as a wet etching process, a dry etchingprocess, a planarization process, combinations thereof, or the like.

In FIGS. 15A and 15B, a memory material layer 90 may be depositedconformally in the trenches 76 along sidewalls and bottom surfaces ofthe trenches 76. The memory material layer 90 may include a materialthat is capable of switching between two different polarizationdirections by applying an appropriate voltage differential across thememory material layer 90. For example, the memory material layer 90includes a high-k dielectric material, such as a hafnium (Hf) baseddielectric materials or the like. In some embodiments, the memorymaterial layer 90 includes hafnium oxide, hafnium zirconium oxide,silicon-doped hafnium oxide, or the like.

In some embodiments, the memory material layer 90 includes bariumtitanium oxide (BaTiO₃), lead titanium oxide (PbTiO₃), lead zirconiumoxide (PbZrO₃), lithium niobium oxide (LiNbO₃), sodium niobium oxide(NaNbO₃), potassium niobium oxide (KNbO₃), potassium tantalum oxide(KTaO₃), bismuth scandium oxide (BiScO₃), bismuth iron oxide (BiFeO₃),hafnium erbium oxide (Hf_(1-x)Er_(x)O), hafnium lanthanum oxide(Hf_(1-x)La_(x)O), hafnium yttrium oxide (Hf_(1-x)Y_(x)O), hafniumgadolinium oxide (Hf_(1-x)Gd_(x)O), hafnium aluminum oxide(Hf_(1-x)Al_(x)O), hafnium zirconium oxide (Hf_(1-x)Zr_(x)O, HZO),hafnium titanium oxide (Hf_(1-x)Ti_(x)O), hafnium tantalum oxide(Hf_(1-x)Ta_(x)O), or a combination thereof, or the like. In someembodiments, the memory material layer 90 include differentferroelectric materials or different types of memory materials. Forexample, the memory material layer 90 is replaced with anon-ferroelectric material, such as a multilayer memory structurecomprising a layer of SiN_(x) between two SiO_(x) layers (e.g., an ONOstructure). In some embodiments, the method of forming the memorymaterial layer 90 includes performing a suitable deposition technique,such as CVD, PECVD, metal oxide chemical vapor deposition (MOCVD), ALD,RPALD, PEALD, MBD or the like.

In some embodiments, the memory material layer 90 has a thickness ofabout 1-50 nm, such as 5-10 nm. Other thickness ranges (e.g., more than20 nm or 5-15 nm) may be applicable. In some embodiments, the memorymaterial layer 90 is formed in a fully amorphous state. In alternativeembodiments, the memory material layer 90 is formed in a partiallycrystalline state; that is, the memory material layer 90 is formed in amixed crystalline-amorphous state and having some degree of structuralorder. In yet alternative embodiments, the memory material layer 90 isformed in a fully crystalline state. In some embodiments, the memorymaterial layer 90 is a single layer. In alternative embodiments, thememory material layer 90 is a multi-layer structure.

After the memory material layer 90 is deposited, an annealing step maybe performed, so as to achieve a desired crystalline lattice structurefor the memory material layer 90. In some embodiments, upon theannealing process, the memory material layer 90 is transformed from anamorphous state to a partially or fully crystalline state. Inalternative embodiments, upon the annealing memory material layer 90 istransformed from a partially crystalline state to a fully crystallinestate.

Then, a channel layer 92 is conformally deposited in the trenches 76over the memory material layer 90. The channel layer 92 includesmaterials suitable for providing channel regions for the memory cells202 (see FIG. 1A). For example, the channel layer 92 includes oxidesemiconductor (OS) such as zinc oxide (ZnO), indium tungsten oxide(InWO), indium gallium zinc oxide (InGaZnO, IGZO), indium zinc oxide(InZnO), indium tin oxide (ITO), combinations thereof, or the like. Insome embodiments, the channel layer 92 includes polycrystalline silicon(poly-Si), amorphous silicon (a-Si), or the like. The channel layer 92may be deposited by CVD, PVD, ALD, PECVD, or the like. The channel layer92 may extend along the sidewalls and the bottom surfaces of thetrenches 76 over the memory material layer 90. After the channel layer92 is deposited, an annealing step may be performed to activate thecharge carriers of the channel layer 92.

In FIGS. 16A and 16B, bottom portions of the memory material layer 90and the channel layer 92 are removed in the trenches 76. In someembodiments, top portions of the memory material layer 90 and thechannel layer 92 are also removed from the multi-layer stack 58. Theremoval process includes an acceptable etching process, such as a dryetch (e.g., RIE, NBE, the like), a wet etch, the like, or a combinationthereof. The etching may be anisotropic. For example, the removalprocess is a blanket etch. In some embodiments, as shown in FIG. 16A,the memory material layer 90 and the channel layer 92 are ring-shaped.From a top view, the memory material layer 90 and the channel layer 92may be any shape such as an oval-like shape, a triangle-like shape, arectangle-like shape and a polygon-like shape according to the shape ofthe trench 76. In some embodiments, bottom inner sidewalls of thechannel layer 92 and the memory material layer 90 are substantiallyflush with each other.

FIGS. 17A through 22B illustrate intermediate steps of manufacturingconductive pillars 106A, 106B and 108 (e.g., source/drain pillars) inthe memory device 200. The conductive pillars 106A, 106B and 108 mayextend along a direction perpendicular to the conductive lines 112 suchthat individual cells of the memory device 200 may be selected for readand write operations. FIGS. 17A, 18A, 19A, 20A, 21A and 22A illustratetop-down views. FIGS. 17B, 18B, 19B, 20B, 21B and 22B are illustratedalong reference cross-section C-C′ illustrated in FIGS. 17A, 18A, 19A,20A, 21A and 22A (also along reference cross-section C-C′ illustrated inFIG. 1A).

In FIGS. 17A and 17B, a sacrificial layer 94 is deposited in thetrenches 76 over the channel layer 92. The sacrificial layer 94 may bepatterned and replaced in subsequent steps to define the conductivepillars 106A (e.g., electrically connected to bit lines), the conductivepillars 108 (e.g., electrically connected to source lines) and theconductive pillars 106B (e.g., electrically connected to bit lines). Insome embodiments, the sacrificial layer 94 includes SiN, Si, polymer,spin-on-carbon, or the like, which is easily removed by a dry etchprocess or a wet etch process and has etching selectivity with respectto the dielectric pillars 102 (which may include silicon oxide, siliconnitride, silicon oxynitride, silicon carbide, aluminum oxide, or thelike), or the like, which is deposited by CVD, PVD, ALD, PECVD, or thelike. The sacrificial layer 94 may extend along the sidewalls and thebottom surfaces of the trenches 76 over the channel layer 92.

In FIGS. 18A and 18B, photoresist patterns 98 and underlying hard maskpatterns 96 are formed over the multi-layer stack 58, the sacrificiallayer 94, the channel layer 92, and the memory material layer 90. Insome embodiments, a hard mask layer and a photoresist layer aresequentially formed over the multi-layer stack 58. The hard mask layermay include, for example, silicon nitride, silicon oxynitride, or thelike, which may be deposited by CVD, PVD, ALD, PECVD, or the like. Thephotoresist layer is formed by a spin-on technique, for example.

Thereafter, the photoresist layer is patterned to form photoresistpatterns 98 and trenches 100 between the photoresist patterns 98. Thephotoresist is patterned by an acceptable photolithography technique,for example. The patterns of the photoresist patterns 98 are thentransferred to the hard mask layer to form hard mask patterns 96 byusing an acceptable etching process, such as by a dry etch (e.g., RIE,NBE, the like), a wet etch, the like, or a combination thereof. Theetching may be anisotropic. Thus, trenches 100 are formed extendingthrough the hard mask layer. Thereafter, the photoresist patterns 98 maybe optionally removed by an ashing process.

In FIGS. 19A and 19B, the patterns of the hard mask patterns 96 aretransferred to the sacrificial layer 94 using one or more acceptableetching processes, such as by a dry etch (e.g., RIE, NBE, the like), awet etch, the like, or a combination thereof. The etching processes maybe anisotropic. Thus, the trenches 100 extend through the sacrificiallayer 94 are accordingly defined.

In FIGS. 20A and 20B, the hard mask patterns 96 are removed. The hardmask patterns 96 may be removed by an acceptable process, such as a wetetching process, a dry etching process, a planarization process,combinations thereof, or the like. Although three trenches 100 areillustrated, any number of trenches 100 may be formed as required.

In FIGS. 21A and 21B, dielectric pillars 102 are formed in the trenches100. In some embodiments, a dielectric layer is deposited over themulti-layer stack 58 filling in the trenches 100. The dielectric layermay include silicon oxide, silicon nitride, silicon oxynitride, siliconcarbide, aluminum oxide, or the like, which is deposited by CVD, PVD,ALD, PECVD, or the like. After deposition, a planarization process(e.g., a CMP, etch back, or the like) may be performed to remove excessportions of the dielectric layer. Then, the dielectric pillars 102 areformed. In the resulting structure, top surfaces of the multi-layerstack 58 (e.g., dielectric layer 52E), the memory material layer 90, thechannel layer 92, the sacrificial layer 94, the dielectric pillars 102may be substantially level (e.g., within process variations). In someembodiments, materials of the sacrificial layer 94 and the dielectricpillars 102 are selected so that they are etched selectively relativeeach other, and materials of the sacrificial layers 53 and thedielectric pillars 102 are selected so that they are etched selectivelyrelative each other. For example, the sacrificial layer 94 and thesacrificial layers 53 include nitride and the dielectric pillars 102include oxide. Other materials are also possible. The sacrificial layer94 and the sacrificial layers 53 may include different materials.

In FIGS. 22A and 22B, the sacrificial layer 94 are removed, so as todefine trenches 104 between the dielectric pillars 102. In someembodiments, the sacrificial layer 94 is removed by an acceptableprocess, such as a wet etching process, a dry etching process or both.

In FIGS. 23A and 23B, the trenches 104 are filled with a conductivematerial to form the conductive pillars 106A, 106B and 108. Theconductive material may include copper, titanium, titanium nitride,tantalum, tantalum nitride, tungsten, ruthenium, aluminum, polysilicon,combinations thereof, or the like, which may be formed using, forexample, CVD, ALD, PVD, PECVD, or the like. After the conductivematerial is deposited, a planarization (e.g., a CMP, etch back, or thelike) may be performed to remove excess portions of the conductivematerial, thereby forming the conductive pillars 106A, 106B and 108. Inthe resulting structure, top surfaces of the multi-layer stack 58 (e.g.,the dielectric layer 52E), the memory material layer 90, the channellayer 92, the dielectric pillars 102, the conductive pillars 106A, theconductive pillars 106B and the conductive pillars 108 may besubstantially level (e.g., within process variations). In someembodiments, the conductive pillars 106A and the conductive pillars 106Bcorrespond to and are electrically connected to the bit lines in thememory device 200, and the conductive pillars 108 correspond tocorrespond to and are electrically connected to the source lines in thememory device 200. In alternative embodiments, the conductive pillars106A and the conductive pillars 106B correspond to and are electricallyconnected to the source lines in the memory device 200, and theconductive pillars 108 correspond to and are electrically connected tothe bit lines in the memory device 200.

In some embodiments, the conductive pillars 106A, 106B and 108 aresurrounded by the channel layer 92 and the memory material layer 90. Forexample, the channel layer 92 and the memory material layer 90 arecontinuously disposed over outer sidewall surfaces of the conductivepillar 106A, the dielectric pillar 102 between the conductive pillar106A and the conductive pillar 106B, the conductive pillar 108, thedielectric pillar 102 between the conductive pillar 108 and theconductive pillar 106B, and the conductive pillar 106B. The channellayer 92 may be in direct contact with the conductive pillars 106A, 106Band 108 and the dielectric pillars 102 therebetween. The memory materiallayer 90 may be continuously disposed on outer sidewall surfaces of thechannel layer 92. In some embodiments, the memory material layer 90 isin direct contact with the outer sidewall surfaces and the bottomsurface of the channel layer 92.

The conductive pillars 106A, 106B are disposed at different sides of theconductive pillar 108. For example, the conductive pillars 106A, 106Bare disposed at opposite sides of the conductive pillar 108. In someembodiments, the conductive pillars 106A, 106B have a decreasing widthat its ends. However, in other embodiments, the conductive pillars 106A,106B have a constant width.

FIGS. 24A through 26B are views of intermediate stages in themanufacturing of a conductive line of the memory device 200, inaccordance with some embodiments. In FIGS. 24A through 26B, the bulkmulti-layer stack 58 is patterned to form trenches 110 therethrough, andsacrificial layers 53 are replaced with conductive materials to definethe conductive lines 112. The conductive lines 112 may correspond toword lines in the memory device 200, and the conductive lines 112 mayfurther provide gate electrodes for the resulting memory cells of thememory device 200. FIGS. 24A and 26A illustrate top-down views. FIGS.24B and 26B are illustrated along reference cross-section D-D′illustrated in FIGS. 24A and 26A (also reference cross-section D-D′illustrated in FIG. 1A), and FIG. 25 is illustrated along referencecross-section D-D′ illustrated in FIG. 24A (also reference cross-sectionD-D′ illustrated in FIG. 1A).

In FIGS. 24A through 24B, the trenches 110 extend through the bulkmulti-layer stack 58. The trenches 110 are formed by using a combinationof photolithography and etching, for example.

In FIG. 25 , the sacrificial layers 53A-53D (collectively referred to assacrificial layers 53) are replaced with conductive lines 112A-112D(collectively referred to as conductive lines 112). In some embodiments,the sacrificial layers 53 are removed by an acceptable process, such asa wet etching process, a dry etching process or both. For example, hotphosphoric acid is used to remove the sacrificial layers 53. Thereafter,conductive lines 112 are filled into the space between two adjacentdielectric layers 52. As shown in the local enlarged view, eachconductive line 112 includes two barrier layers 114 and 118 and a metallayer 116 between the barrier layers 114 and 118. Specifically, thebarrier layer 114 or 118 is disposed between the metal layer 116 and theadjacent dielectric layer 52. The barrier layers 114 and 118 may preventthe metal layer from diffusion to the adjacent dielectric layers 52. Thebarrier layers 114 and 118 may also provide the function of increasingthe adhesion between the metal layer 116 and the adjacent dielectriclayers 52, and may be referred to as glue layers in some examples. Insome embodiments, both barrier layers and glue layers with differentmaterials are provided as needed. The barrier layers 114 and 118 areformed of a first conductive material, such as a metal nitride, such astitanium nitride, tantalum nitride, molybdenum nitride, zirconiumnitride, hafnium nitride, or the like. The metal layer 116 may areformed of a second conductive material, such as a metal, such astungsten, ruthenium, molybdenum, cobalt, aluminum, nickel, copper,silver, gold, alloys thereof, or the like. The barrier layers 114, 118,and metal layer 116 may each be formed by an acceptable depositionprocess such as CVD, PVD, ALD, PECVD, or the like. The first conductivematerial of the barrier layers 114, and 118, and the second conductivematerial of the metal layer 116 are further deposited on the sidewallsof the multi-layer stack 58 and fill in the trenches 110. Thereafter,the first conductive material of the barrier layers 114, and 118, andthe second conductive material of the metal layer 116 in the trenches110 are removed by an etching back process and/or a pull back process toavoid the short between the conductive lines 112. An acceptable etchback process and/or a pull back process may be performed to removeexcess materials from the sidewalls of the dielectric layers 52 andbottom surfaces of the trenches 110. The acceptable etch back processand/or a pull back process may include a dry etch (e.g., RIE, NBE, thelike), a wet etch, the like, or a combination thereof. The acceptableetch back process and/or a pull back process may be anisotropic.

In FIGS. 26A and 26B (in FIG. 26A, the dielectric layer 52E is omittedfor clarity), dielectric layers 120 are formed in the trenches 110 toisolate the adjacent common conductive lines 112. In some embodiments, adielectric layer is deposited over the multi-layer stack 58 filling inthe trenches 110. The dielectric layer may include, for example, siliconoxide, silicon nitride, silicon oxynitride, or the like, which may bedeposited by CVD, PVD, ALD, PECVD, or the like. The dielectric layer mayextend along sidewalls and bottom surfaces of the trenches 110. Afterdeposition, a planarization process (e.g., a CMP, etch back, or thelike) may be performed to remove excess portions of the dielectriclayer. In the resulting structure, top surfaces of the multi-layer stack58 (e.g., dielectric layer 52E), the memory material layer 90, thechannel layer 92, and the dielectric layers 120 may be substantiallylevel (e.g., within process variations).

In some embodiments, upon the replacement process, the sacrificiallayers 53 of the strip-shaped staircase structures are subsequentlyreplaced with conductive lines 112 (see FIG. 1A).

Thus, stacked memory cells 202 may be formed in the memory device 200,as shown in FIG. 1A. Each memory cell 202 includes a gate electrode(e.g., a portion of a corresponding conductive line 112), a gatedielectric (e.g., a portion of a corresponding memory material layer90), a channel region (e.g., a portion of a corresponding channel layer92), and source/drain pillars (e.g., portions of correspondingconductive pillars 106A, 106B and 108). The memory cells 202 may bedisposed in an array of vertically stacked rows and columns. In someembodiments, adjacent rows of the memory cells 202 share a commonconductive line 112 (e.g., word line) therebetween, and the commonconductive lines 112 are isolated by the dielectric layers 120therebetween. However, the disclosure is not limited thereto.

In FIGS. 27A, 27B, 27C and 27D, an IMD layer 121 is formed on topsurfaces of the multi-layer stack 58 (e.g., the dielectric layer 52E),the memory material layer 90, the channel layer 92, the conductivepillars 106A, 106B, the conductive pillars 108 and the IMD 70.Conductive contacts 122A, 122B, 124 and 126 are made on the conductivelines 112, the conductive pillars 106A, 106B, and the conductive pillars108, respectively. FIG. 27A illustrates a perspective view of the memorydevice 200; FIG. 27B illustrates a cross-sectional view of the devicealong line C-C′ of FIG. 1A; FIG. 27C illustrates a cross-sectional viewof the device along line E-E′ of FIG. 27A; and FIG. 27D illustrates across-sectional view of the device along line B-B′ of FIG. 1A.

The IMD 121 may be formed of a dielectric material, and may be depositedby any suitable method, such as CVD, PECVD, flowable CVD (FCVD), or thelike. The dielectric materials may include phospho-silicate glass (PSG),boro-silicate glass (BSG), boron-doped phospho-silicate glass (BPSG),undoped silicate glass (USG), a low-k dielectric material or the like.In some embodiments, the IMD 121 may include an oxide (e.g., siliconoxide or the like), a nitride (e.g., silicon nitride or the like), acombination thereof or the like. Other dielectric materials formed byany acceptable process may be used. Thereafter, a removal process isapplied to the IMD 121 to remove excess dielectric material over themulti-layer stack 58 and the IMD 70. In some embodiments, the removalprocess may be a planarization process, such as a chemical mechanicalpolish (CMP), an etch-back process, combinations thereof, or the like.

In some embodiments, the staircase shape of the conductive lines 112provides a surface on each of the conductive lines 112 for theconductive contacts 126 to land on. In some embodiments, forming theconductive contacts 126 may include patterning openings in the IMD 121and IMD 70 to expose portions of the conductive lines 112 using acombination of photolithography and etching, for example. A liner (notshown), such as a diffusion barrier layer, an adhesion layer, or thelike, and a conductive material are formed in the openings. The linermay include titanium, titanium nitride, tantalum, tantalum nitride, orthe like. The conductive material may include copper, a copper alloy,silver, gold, tungsten, cobalt, aluminum, nickel, or the like. Aplanarization process, such as a CMP, may be performed to remove excessmaterial from the surface of the IMD 121. The remaining liner andconductive material form the conductive contacts 126 in the openings.

As also illustrated by the perspective view of FIG. 27A, conductivecontacts 122A, 122B and 124 may also be made on the conductive pillars106A, 106B and the conductive pillars 108, respectively. The conductivecontacts 122A, 122B, 124 and 126 may be electrically connected toconductive lines 128A1, 128A2, 128B and 128C, respectively, whichconnect the memory array to an underlying/overlying circuitry (e.g.,control circuitry) and/or signal, power, and ground lines in thesemiconductor die. For example, as shown in FIG. 27C, the conductivecontacts 126 extend through the IMD 121 and IMD 70 to electricallyconnect conductive lines 128C to the conductive lines 112. Otherconductive contacts or vias may be formed through the IMD 121 toelectrically connect the conductive lines 128A1, 128A2, 128B and 128C tothe underlying active devices on the substrate. In alternativeembodiments, routing and/or power lines to and from the memory array maybe provided by an interconnect structure formed over the memory device200 in addition to or in lieu of the interconnect structure 320.Accordingly, the memory device 200 may be completed. In someembodiments, a common conductive pillar (i.e., the conductive pillar108) electrically connected to a common source line is disposed betweentwo conductive pillars (i.e., the conductive pillars 106A, 106B)electrically connected to bit lines. In this configuration, by changingthe source line/bit line voltage, the trapped charge may be addressed to4 bits in one memory cell. That is, the memory cell 202 is operated as a4-bits memory cell, for example. Thus, the operation speed of the memorycell is faster, and the device performance is accordingly improved.

Although the embodiments of FIGS. 1A through 27B illustrate a particularpattern for the conductive pillars 106A, 106B and 108, otherconfigurations are also possible. For example, in these embodiments, theconductive pillars 106A, 106B and 108 have a staggered pattern. However,in other embodiments, the conductive pillars 106A, 106B and 108 in asame row of the array are all aligned with each other, as shown in thememory device 200A of FIG. 28 .

In some embodiments, adjacent rows of the memory cells 202 share acommon conductive line 112 (e.g., word line) therebetween. However, thedisclosure is not limited thereto. In alternative embodiments, as shownin the memory device 200B of Figure FIGS. 29A and 29B, separatedconductive lines 112 (e.g., word lines) are formed for each row of thememory cells 202, and dielectric layers 130 are disposed between andisolates adjacent sets of the conductive pillars 106A, 106B and 108.FIGS. 30A to 30C illustrate varying top down views of manufacturing amemory device in accordance with some embodiments, and the dielectriclayer 52E is omitted for clarity. In such embodiments, as shown in FIG.30A, after forming the multi-layer stack 58 as shown in FIG. 12 , aplurality of trenches are formed, and then the trenches are filled withdielectric layers 130. In some embodiments, the dielectric layers 130include silicon nitride. Then, as shown in FIG. 30B, conductive pillars106A, 106B and 108, dielectric pillars 102 and memory material layer 90,channel layer 92 are formed. Thereafter, as shown in FIG. 30C, aplurality of trenches 107 are formed in the dielectric layers 130, andthe sacrificial layers 53 are replaced with conductive materials throughthe trenches 107, to define the conductive lines 112. This step issimilar to FIG. 25 . After the conductive lines 112 are formed,dielectric layers 132 are formed in the trenches 107. In someembodiments, a material of the dielectric layers 132 is the same as amaterial of dielectric layers 130. However, the disclosure is notlimited.

In some embodiments, the conductive pillars 106A, 106B and 108 arearranged as an oval-like shape. In alternative embodiments, theconductive pillars 106A, 106B and 108 are arranged to form other shapesuch as a rectangular shape, as shown in FIG. 31 . In such embodiments,the conductive pillars 106A and 106B are disposed at opposite sides ofthe conductive pillar 108. The conductive pillars 106A, 106B may beelectrically connected to first conductive lines (e.g., the bit lines),and the conductive pillar 108 may be electrically connected to secondconductive line (e.g., the source line). In alternative embodiments, theconductive pillars 106A, 106B are electrically connected to the sourcelines, and the conductive pillar 108 is electrically connected to thebit line. In above embodiments, three conductive pillars 106A, 106B and108 are illustrated. However, other embodiments may include othernumbers of the conductive pillars. For example, in FIG. 32 , there arefour conductive pillars 106A, 106B, 108A and 108B. The conductivepillars 108A and 108B are disposed between the conductive pillars 106Aand 106B. The conductive pillars 106A, 106B may be electricallyconnected to first conductive lines (e.g., the bit lines), and theconductive pillars 108A, 108B may be electrically connected to secondconductive lines (e.g., the source lines). In alternative embodiments,the conductive pillars 106A, 106B are electrically connected to thesource lines, and the conductive pillars 108A, 108B are electricallyconnected to the bit lines.

In some embodiments, as shown in FIGS. 33 and 34 , there are fourconductive pillars 106A, 106B, 106C and 108. The central conductivepillar (e.g., the conductive pillar 108) is a polygon column, and otherconductive pillars (e.g., the conductive pillars 106A, 106B, 106C) aredisposed at different sides of the polygon column respectively. Forexample, as shown in FIG. 33 , the conductive pillar 108 is a triangularcolumn, and the conductive pillars 106A, 106B, 106C are disposed at allsides of the conductive pillar 108 respectively. The conductive pillars106A, 106B, 106C may be electrically connected to first conductive lines(e.g., the bit lines), and the conductive pillar 108 may be electricallyconnected to a second conductive line (e.g., the source line). Inalternative embodiments, the conductive pillars 106A, 106B, 106C areelectrically connected to the source lines, and the conductive pillar108 is electrically connected to the bit line. In some embodiments, asshown in FIG. 34 , the conductive pillar 108 is a hexagonal column, andthe conductive pillars 106A, 106B, 106C are disposed at three sides ofthe conductive pillar 108 respectively. The conductive pillars 106A,106B, 106C may be electrically connected to first conductive lines(e.g., the bit lines), and the conductive pillar 108 may be electricallyconnected to a second conductive line (e.g., the source line). Inalternative embodiments, the conductive pillars 106A, 106B, 106C areelectrically connected to the source lines, and the conductive pillar108 is electrically connected to the bit line.

In FIGS. 31 to 34 , the conductive pillars are surrounded by the channellayer 92 and the memory material layer 90. For example, the channellayer 92 and the memory material layer 90 are continuously disposed overouter sidewall surfaces of the conductive pillars (e.g., the conductivepillars 106A, 106B, 106C, 108A, 108B), the dielectric pillar 102 betweenadjacent ones of the conductive pillars (e.g., the conductive pillars106A, 106B, 106C, 108A, 108B). The channel layer 92 may be in directcontact with the conductive pillars (e.g., the conductive pillars 106A,106B, 106C, 108A, 108B) and the dielectric pillars 102 therebetween. Thememory material layer 90 may be continuously disposed on outer sidewallsurfaces of the channel layer 92, and the memory material layer 90 maybe in direct contact with the outer sidewall surfaces of the channellayer 92. Although corners of the conductive pillars (e.g., theconductive pillars 106A, 106B, 106C, 108A, 108B) are illustrated assharp corners, the corners of the conductive pillars (e.g., theconductive pillars 106A, 106B, 106C, 108A, 108B) may be rounded corners.By these configurations of FIGS. 31 to 34 , by changing the sourceline/bit line voltage, the trapped charge may be addressed to more thantwo bits in one memory cell. That is, the memory cell is operated as amultiple-bits memory cell, for example. Thus, the operation speed of thememory cell is faster, and the device performance is accordinglyimproved.

FIG. 35 illustrates a method of forming a memory device in accordancewith some embodiments. Although the method is illustrated and/ordescribed as a series of acts or events, it will be appreciated that themethod is not limited to the illustrated ordering or acts. Thus, in someembodiments, the acts may be carried out in different orders thanillustrated, and/or may be carried out concurrently. Further, in someembodiments, the illustrated acts or events may be subdivided intomultiple acts or events, which may be carried out at separate times orconcurrently with other acts or sub-acts. In some embodiments, someillustrated acts or events may be omitted, and other un-illustrated actsor events may be included.

At act S400, a multi-layer stack is formed on a substrate, and themulti-layer stack includes a plurality of dielectric layers and aplurality of first sacrificial layers stacked alternately and has aplurality of first trenches penetrating therethrough. FIG. 4 to FIG. 14Billustrate varying views corresponding to some embodiments of act S400.

At act S402, a plurality of memory material layers are formed alongsidewalls and bottom surfaces of the first trenches. FIG. 15A to FIG.16B illustrate varying views corresponding to some embodiments of actS402.

At act S404, a plurality of channel layers are formed over the memorymaterial layers along the sidewalls and the bottom surfaces of the firsttrenches. FIG. 15A to FIG. 16B illustrate varying views corresponding tosome embodiments of act S404.

At act S406, a plurality of second sacrificial layers are formed to fillthe first trenches respectively. FIG. 17A and FIG. 17B illustrates across-sectional view corresponding to some embodiments of act S406.

At act S408, a plurality of second trenches are formed in each of theplurality of second sacrificial layers. FIG. 18A to FIG. 19B illustratevarying views corresponding to some embodiments of act S408.

At act S410, a plurality of dielectric pillars are formed in the secondtrenches respectively. FIG. 21A and FIG. 21B illustrate varying viewscorresponding to some embodiments of act S410.

At act S412, the remaining second sacrificial layer is replaced with aplurality of conductive pillars. FIG. 22A and FIG. 23B illustratevarying views corresponding to some embodiments of act S412.

At act S414, the first sacrificial layers are replaced with a pluralityof conductive lines. FIG. 24A and FIG. 25B illustrate varying viewscorresponding to some embodiments of act S414.

In some embodiments of the disclosure, a stackable 3D non-volatilememory (NVM) architecture is formed to provide an ultra-high density,and all memory cells in the 3D array are connected in parallel. Thus, asum-of-product operation is enabled. In some embodiments of thedisclosure, the cell is formed with a common source line. For example,more than 2 bits are formed in each memory cell. In some embodiments, 2n(n is an integer larger than 1) bits is formed per cell. Thus, theoperation speed of the memory cell is faster, and the device performanceis accordingly improved.

In the above embodiments, the memory device is formed by a “staircasefirst process” in which the staircase structure is formed before thememory cells are formed. However, the disclosure is not limited thereto.In other embodiments, the memory device may be formed by a “staircaselast process” in which the staircase structure is formed after thememory cells are formed.

In the above embodiments, the gate electrodes (e.g., word lines) areformed by depositing sacrificial dielectric layers followed by replacingsacrificial dielectric layers with conductive layers. However, thedisclosure is not limited thereto. In other embodiments, the gateelectrodes (e.g., word lines) may be formed in the first stage withoutthe replacement step as needed.

In accordance with some embodiments of the present disclosure, a memorydevice includes a multi-layer stack, a channel layer, a memory materiallayer and at least three conductive pillars. The multi-layer stack isdisposed on a substrate and includes a plurality of conductive layersand a plurality of dielectric layers stacked alternately. The channellayer penetrates through the plurality of conductive layers and theplurality of dielectric layers. The memory material layer is disposedbetween the channel layer and each of the plurality of conductive layersand the plurality of dielectric layers. The conductive pillars aresurrounded by the channel layer and the memory material layer, whereinthe at least three conductive pillars are electrically connected toconductive lines respectively.

In accordance with alternative embodiments of the present disclosure, amemory device includes a multi-layer stack, a first conductive pillar, aplurality of second conductive pillars, a plurality of dielectricpillars, a channel layer and a memory material layer. The multi-layerstack is disposed on a substrate and includes a plurality of gateelectrode layers and a plurality of dielectric layers stackedalternately. The first conductive pillar penetrates through themulti-layer stack. The second conductive pillars are at different sidesof the first conductive pillar. The first conductive pillar and thesecond conductive pillars are electrically connected to conductive linesrespectively. The dielectric pillars penetrate through the multi-layerstack and disposed between the first conductive pillar and each of thesecond conductive pillars. The channel layer surrounds the firstconductive pillar, the second conductive pillars and the dielectricpillars. The memory material layer is disposed between the channel layerand the multi-layer stack.

In accordance with yet alternative embodiments of the presentdisclosure, a method of forming a memory device includes the followingsteps. A multi-layer stack is formed on a substrate, wherein themulti-layer stack comprises a plurality of dielectric layers and aplurality of first sacrificial layers stacked alternately and has aplurality of first trenches penetrating therethrough. A plurality ofmemory material layers are formed along sidewalls and bottom surfaces ofthe plurality of first trenches. A plurality of channel layers areformed over the plurality of memory material layers along the sidewallsand the bottom surfaces of the plurality of first trenches. A pluralityof second sacrificial layers are formed to fill the plurality of firsttrenches respectively. A plurality of second trenches are formed in eachof the plurality of second sacrificial layers. A plurality of dielectricpillars are formed in the plurality of second trenches respectively. Theremaining second sacrificial layer is replaced with a plurality ofconductive pillars respectively. The plurality of first sacrificiallayers are replaced with a plurality of conductive lines respectively.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A memory device, comprising: a multi-layer stack,disposed on a substrate and comprising a plurality of conductive layersand a plurality of dielectric layers stacked alternately along a firstdirection; a channel layer, penetrating through the plurality ofconductive layers and the plurality of dielectric layers; a memorymaterial layer, disposed between the channel layer and each of theplurality of conductive layers and the plurality of dielectric layers;and at least three conductive pillars, extending in the first direction,surrounded by the channel layer and the memory material layer, whereinthe at least three conductive pillars are electrically connected toconductive lines respectively, and the at least three conductive pillarsare aligned along a second direction substantially perpendicular to thefirst direction.
 2. The memory device of claim 1, wherein the at leastthree conductive pillars include first conductive pillars electricallyconnected to bit lines respectively and a second conductive pillarbetween the first conductive pillars and electrically connected to asource line.
 3. The memory device of claim 1 further comprising adielectric material between each adjacent two of the at least threeconductive pillars.
 4. The memory device of claim 1, wherein the channellayer is a continuous layer that surrounds outer sidewalls of the atleast three conductive pillars.
 5. The memory device of claim 1, whereinthe memory material layer is a continuous layer that surrounds outersidewalls of the at least three conductive pillars.
 6. The memory deviceof claim 1 further comprising a plurality of dielectric pillars, whereinthe dielectric pillars and the at least three conductive pillars arealternately disposed, and the dielectric pillars are physicallyseparated by one of the at least three conductive pillars disposedbetween the dielectric pillars.
 7. A memory device, comprising: amulti-layer stack, disposed on a substrate and comprising a plurality ofgate electrode layers and a plurality of dielectric layers stackedalternately; a first conductive pillar, penetrating through themulti-layer stack; a plurality of second conductive pillars at differentsides of the first conductive pillar, wherein the first conductivepillar and the second conductive pillars are electrically connected toconductive lines respectively; a channel layer, wherein the channellayer is a continuous layer that surrounds outer sidewalls of the firstconductive pillar, and the second conductive pillars; and a memorymaterial layer, disposed between the channel layer and the multi-layerstack.
 8. The memory device of claim 7, wherein the second conductivepillars are disposed at opposite sides of the first conductive pillar.9. The memory device of claim 7, wherein the first conductive pillar issurrounded by the second conductive pillars.
 10. The memory device ofclaim 7, wherein the first conductive pillar is a polygon column, andthe second conductive pillars are disposed at all sides of the polygoncolumn respectively.
 11. The memory device of claim 7, wherein the firstconductive pillar is electrically connected to a source line, and thesecond conductive pillar are electrically connected to bit linesrespectively.
 12. The memory device of claim 7 further comprising aplurality of dielectric pillars, penetrating through the multi-layerstack and disposed between the first conductive pillar and each of thesecond conductive pillars, wherein the channel layer further surroundsouter sidewalls of the dielectric pillars.
 13. A method of forming amemory device, comprising: forming a multi-layer stack on a substrate,wherein the multi-layer stack comprises a plurality of dielectric layersand a plurality of first sacrificial layers stacked alternately along afirst direction and has a plurality of first trenches penetratingtherethrough; forming a plurality of memory material layers alongsidewalls and bottom surfaces of the plurality of first trenches;forming a plurality of channel layers over the plurality of memorymaterial layers along the sidewalls and the bottom surfaces of theplurality of first trenches; forming a plurality of second sacrificiallayers to fill the plurality of first trenches respectively; forming aplurality of second trenches in each of the plurality of secondsacrificial layers; forming a plurality of dielectric pillars in theplurality of second trenches respectively; replacing the remainingsecond sacrificial layers with a plurality of conductive pillarsrespectively, wherein the conductive pillars comprise at least threeconductive pillars, and the at least three conductive pillars arealigned along a second direction substantially perpendicular to thefirst direction; and replacing the plurality of first sacrificial layerswith a plurality of conductive lines respectively.
 14. The method ofclaim 13 further comprising: removing portions of the multi-layer stackbetween the plurality of first trenches, to form a plurality of thirdtrenches; and forming a plurality of isolation pillars in the pluralityof third trenches respectively.
 15. The method of claim 14, wherein theplurality of isolation pillars have an etching selectivity with respectto the plurality of first sacrificial layers during replacing theplurality of first sacrificial layers with the plurality of conductivelines.
 16. The method of claim 13, wherein the plurality of dielectricpillars have an etching selectivity with respect to the plurality offirst sacrificial layers during replacing the plurality of firstsacrificial layers with the plurality of conductive lines.
 17. Themethod of claim 13, wherein replacing the remaining second sacrificiallayers with the plurality of conductive pillars comprises: removing theremaining second sacrificial layers, to form a plurality of thirdtrenches between the plurality of dielectric pillars; forming aconductive material to fill the plurality of third trenches; andremoving the conductive material outside the plurality of thirdtrenches, to form the plurality of conductive pillars in the pluralityof third trenches respectively.
 18. The method of claim 13, whereinreplacing the plurality of first sacrificial layers with the pluralityof conductive lines comprises: forming a plurality of third trenches inthe multi-layer stack; removing the plurality of first sacrificiallayers; and forming the plurality of conductive lines into spacesbetween the plurality of dielectric layers.
 19. The method of claim 13,wherein forming the plurality of channel layers, the plurality of memorymaterial layers and the second sacrificial layers comprise: forming achannel material along the sidewalls and the bottom surfaces of theplurality of first trenches and top surfaces of the multi-layer stackbetween the plurality of first trenches; forming a memory material overthe channel material along the sidewalls and the bottom surfaces of theplurality of first trenches and over the top surfaces of the multi-layerstack between the plurality of first trenches; forming a sacrificialmaterial over the memory material to fill the plurality of firsttrenches; and removing the channel material, the memory material and thesacrificial material outside the plurality of first trenches.
 20. Themethod of claim 13, wherein a top view of the plurality of firsttrenches is ring-shaped.